Java : Servlet Tutorials

History of Web application
Earlier in client- server computing, each application had its own client program and it worked as a user interface and need to be installed on each user's personal computer.

Java : Servlet Tutorials

Java Servlets it Java technology for creating the dynamic web applications.
Java Servlets are server side components in Java that runs on Servlet enabled
web server such as Tomcat, Jetty, Websphere etc.. Java Servlet is much faster
then CGI and Perl since it runs in the same JVM. In case of CGI and Perl
separate memory space is allocated for execution of the program which reduces
it's performance.

For running the Java Servlet you can download the latest version of Tomcat
server and install on your computer. It's much easier to use Tomcat for learning
Java Servlet. These step-by-step tutorials will teach you Java Servlet and
impart the knowledge necessary for developing and testing Java Servlet. After
learning these tutorials you will be able to start using Java Servlet in your
web projects.

In this section you will find several tutorials of Java Servlet.

First let's understand about web and web applications.

History of Web
applicationEarlier in client- server computing, each application had its own
client program and it worked as a user interface and need to be
installed on each user's personal computer.

Introduction
to Web ServerWeb Server is a computer on the World Wide Web that
stores Html documents that can be retrieved via a Web browser. It is a
computer that delivers web pages.

What
is a Container
Container are nothing but a Java application which controls servlets.
Tomcat is one of the example of a container. It is the container which
calls the servlet's methods like doPost() and doGet().

After understanding the basics of web and web application development we will
learn about the Servlet technology of Java. The Servlet technology helps the
developer to write dynamic web applications. JSP is also compiled into Servlet
before it is executed on the container.

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Let's get started with the Servlet technology. You can learn Java Servlet here with help of example programs given below:

How to run a
Servlet?Install the tomcat server in a directory in which you want to install
and set the classpath.for the variable JAVA_HOME in the environment
variable.

Writing Hello WorldWe should start understanding the servlets from the beginning. Lets
start by making one program which will just print the "Hello
World" on the browser. Each time the user visits this page it will
display "Hello World" to the user.

Displaying
Date in ServletIn this example we are going to show how we can display a current date
and time on our browser. It is very easy to display it on our browser by
using the Date class of the java.util package.

Simple Counter In ServletIn this example we are going to know how we can make a
program on counter which will keep track how many times the servlet has been
accessed.

A
Holistic counter in ServletIn this program we are going to make a such a servlet which will count
the number it has been accessed and the number of threads created by the
server.

Counter in
Init() MethodIn this program we are going to make a such a servlet which will count
and displays the number of times it has been accessed and by reading the
init parameter to know from where the counting will begin.

Snooping
the serverTo display the name of the server you are using use the method getServerName()
of the ServletRequest interface. To display the server
port number use the method getServerPort().

Snooping HeadersIn this program we are going to going to make a servlet
which will retrieve all the Http request header.

Dice RollerWe are going to make one program on the dice roller in
which the number in the dice will be selected randomly.

Getting Init Parameter NamesWhenever the container makes a servlet it always reads it deployment
descriptor file i.e. web.xml. Container creates name/value pairs for the
ServletConfig object. Once the parameters are in ServletConfig they will
never be read again by the Container.

Time Updater in Servlet
In this program we are going to make one program on
servlet which will keep on updating the time in every second and the result will
be displayed to you.

Send Redirect in Servlet
In this example we are going to make one html in which
we will submit the user name and his password. The controller will check if the
password entered by the user is correct or not.

Session Tracking
As we know that the Http is a stateless
protocol, means that it can't persist the information. It always treats each
request as a new request. In Http client makes a connection to the server, sends
the request., gets the response, and closes the connection.

Pre- Existing Session
In this example we are going to find out whether the
session is pre- existing or not.

Session Last Accessed Time Example
This example illustrates to find current access time of session
and last access time of session. Sessions are used to maintain state and user
identity across multiple page requests.

Get Session Id
In this example we are going to make a program in which we will find the
session id which was generated by the container.

Display session value Using Servlet
Sometime while developing web application it is necessary to interact with
the different values of the Session object. In this example we will explore the different
values of the Session object and then learn how to use it in our programming
code.

Hit Counter Servlet Example
This example illustrates about counting how many times the servlet is
accessed. When first time
servlet (CounterServlet) runs then session is created and value of the counter will be zero and after
again accessing of servlet the counter value will be increased by one.

Getting Columns Names using Servlets
Consider a situation where there is a need to know
about the name of the columns without touching our database. As we are the
programmers so why we need to worry about the database.

Getting Number of ColumnsConsider a situation where there is a need to know
about the number of columns in the table without touching our database. As we
are the programmers so why we should worry about the database.

Getting Number of RowsConsider a situation where we want to know about the
number of rows in the particular database table without touching our database. We want to find out the number of rows without going touching our
back- end.

Deleting Rows From Table
Consider a situation where we have entered some wrong
data and in later situation it starts giving problem to the organization.

Deleting
All Rows From the database Table
Consider a situation where we have entered some wrong
data and in later situation it starts giving problem to an organization or
may become useless after sometime . Rather than go
through with that data its better to delete that data.

How to add a column in a table
Consider a situation where the requirement
of the client gets changed and you have asked to modify the structure of
the table. In reality it is the work of the database administrator but
as a Java programmer you should know how you can modify the structure of
the table.

Get
And Post Method of HttpThe Get is one the simplest Http method. Its main job is to ask the
server for the resource. The Post method is more powerful request. By
using Post we can request as well as send some data to the server.

Servlets Links
Servlets are the Java platform technology of choice for extending and
enhancing Web servers. Servlets provide a component-based,
platform-independent method for building Web-based applications, without
the performance limitations of CGI programs. And unlike proprietary
server extension mechanisms (such as the Netscape Server API or Apache
modules), servlets are server- and platform-independent.

Select Color
In this program we are going to selected the various
color and on the basis of the selection the output will be displayed to the
user.

sendRedirect
In send Redirect whenever the client makes any request
it goes to the container, there the container decides whether the concerned
servlet can handle the request or not.

Send Redirect in Servlet
When we want that someone else should handle the
response of our servlet, then there we should use sendRedirect() method.

Random
RedirectorIn this program we are going to make such a servlet which will be
responsible to select a site randomly from the list of sites you have
entered. Note that the selection of the site will be randomly.

Servlet
ContextServletContext is a interface which helps
us to communicate with the servlet container. There is only one ServletContext
for the entire web application and the components of the web application can
share it.

ServletContextListener
exampleServletContextListener is notified when the
context is initialized. It will be notified when the context is
destroyed. It closes the database connection.

ServletContextAttributeListenerThe listener ServletContextAttributeListener
is an interface and extends the java.util.EventListener class. This
listener come into existence when this interface receives notifications of
changes to the attribute list on the servlet context of a web application.

HttpSessionListenerHttpSessionListener is an interface
which extends java.util.EventListener class. The main purpose of
this listener is to notify whenever there is a change in the list of
active sessions in a web application..

HttpSessionListener
example
Before going into the details of the SessionListener
we should firstly know about the sessions. Whenever a client makes a
request for any resources to the server, the server receives the request
and processes the request and sends back the response.

HttpSessionAttributeListener
The listener HttpSessionAttributeListener
is an interface and extends the java.util.EventListener class. This
listener will be called by the container whenever there there will be change to
the attribute list on the servlet session of a web application.

HttpSessionAttributeListener
Example
This listener is used when we want to know when a attribute has been added in a
session, when a attribute has been removed and when it is replaced by another
attribute.

httpsessionbindinglistenerHttpSessionBindingListener is a interface
which extends java.util.EventListenerinterface. The purpose of
the this interface is to notify an object when it is bound to or unbound from a
session.

Insert Image into Database Using Servlet
This example illustrate the process of inserting image into database table using
Servlet. This type of program is useful in social networking or HR application
where it is necessary to save the uploaded photograph of the user.

Retrieve image from database using ServletIn this example we will show you how to develop a
Servlet that connects to the MySQL database and retrieves the image from the
table. After completing this tutorial you will be able to develop program for
your java based applications that retrieves the image from database.

say hello in spanish
In this program we are going to display
"hello" in spanish along with the date.

Accessing Date In ServletIn this example, we are
going to show how we can display a creation date of the session and last accessed date or time and
id on our browser. It is very easy to display it on our browser by using the Date
class of the java.util package.

Post Message In servletIn this example, we are going to implement posting
massage to servlet. In the following program, you will learn how to post massage.

Show Parameter In ServletIn this section, you will
learn how to send and put all parameter names into the table. Thefollowing program uses two methods, which is described below.

Get Parameter Name From Servlet Request
This example illustrates about how to get parameter from jsp page in your
servlet. In the jsp (parameter.jsp) page we have taken three input fields
having name as firstname,
lastname and middle name..

How to connect to MySql Database from
Servlet?
In this example we will show you how to connect to
MySQL database and perform select operation. You will learn the JDBC steps
necessary to connect to the MySQL Database and execute the query.

Servlet Error Message based on user input
In this example user is presented with a screen to enter the name. If the
entered name exists in the database its displays the sucess message otherwise it
displays the error message. So, you can use Servlet to check the user input
against database and display the message to the user.

Quintessential Servlet
Quintessential servlet is not any special kind of servlet. It is just a
proper and appropriate way to write a servlet. This quintessential servlet means
that servlet is having accurate way of code written for an organizations servlet.

Logging Filter Servlet Example
This example illustrates how one can write Logging Filter servlet to provide
control over log file. You can have additional controls over these log files and
these all are available to use by implementing "Filter" class.

Context Log Example Using Servlet
This example illustrates about how to use of Context Log in
servlet. Context
Log is used to write specified message to server log file when servlet is
called. In the following JSP page (message.jsp) we have simply taken a text area where
user give his/her message and post the form.

Response Filter Servlet ExampleThis Example shows how to use of response filter in Java
Servlet.
Filter reads
own initial parameters and adds its value to the response. Use the init-param child element of
the filter element to declare the initialization parameter and its value.

IP Filter Example
The filter provides a basic security mechanism for a firewall to
determining what traffic passes through the firewall based on IP address
details. This protects the secure network from outsiders.

Working with Tomcat Server
Apache Tomcat is a famous Servlet container developed at
Apache Software Foundation.
This software is released under under the Apache Software
License.

Use of Cookie in Servlet
The cookie class provides an easy way
for servlet to read, create, and
manipulate HTTP-style cookies, which allows servlets to store small amount
of data.

Send a Response Status in servletAll Response status is defined in HttpServletResponse Class. You can
then use constants (response.SC_OK,response.SC_NOT_FOUND
etc..) values to return process status to the browser.

Read Cookies from
ServletsThe Cookie Class provides an easy way to read Cookies. You can use getCookies()
method to retrieve all the cookies in your servlet program.

Send Cookies in Servlets
This section illustrates you how to send cookie in servlets. Cookies are small bits of information that a Web server sends to a
browser and that the browser returns unchanged after visiting the same page.

How to read text file in ServletsIn this example we will use the input stream to read the text from the disk
file. The InputStreamReader class is used to read the file in servlets program.

Check if parameter exists in servlets
requestIn this example we will see how to check is parameter
exists in servlets request. In this example given below we have used method
getParamaterNames() of the ServletRequest interface to find all the
parameters name in the clients request.

Accept Language and Accept Charset in ServletsAccept Language and Accept Char set provides a
servlets to determine the
language in which it will speak to the clients. A browser sends the user's
language to the server using the Accept .

Multiple Drop Down Menu UsingIn this Example we can Add and Update the Details of
Employee using Servlet. We create four file employee.jsp, viewdata.jsp,
EmployeeAdd.java
and viewdata.java.

How to get client's address in a servlet
This is detailed java code to get
client's address in a servlet. In this example we have used method getremoteAddr()
of the ServletRequest interface which returns IP address of the client in the
string format.

Search from Database In ServletIn this section, we have developed an Employee Search application. We created
three file search.jsp, viewSearch.jsp and Search.java.

ServletContextListener with TimerIn this section, you will learn how to use timer with ServletContextListener
to run code snippet after every 1 minute immediate after the application run. In the below
eaxmple, we are using ServletContextListener with timer to
run code after every 1 min. ServletContextListener immediately
starts after code execution. And the Timer class of java.util.Timer
is used inside contextInitialized() function, which runs the
code after every 1 minute.

iica
December 7, 2011
dropdown example gender
Here's my code.
out.println("<td>Gender:</td>");
out.println("<td><select name='gender' ><option>"+rs.getString(7)+"</option><option>Male</option><option>Female</option></select></td>");
This displays the result and the gender option Male and Female. I want to know if I can use an if statement that when Female is selected as the gender, Male should be left in the drop down.

Joyce
June 15, 2013
vhdVzUIIvB
That insgiht's just what I've been looking for. Thanks!

Ankit
October 20, 2012
Java servlet
Here, This site provides very useful information for java begineers to learn the every topic in deatil.
You can find article for Java Servlet here..
http://techdistance.com/java-servlet-basic-tutorial-with-example/